I think you are describing the crankcase breather tube.. maybe.. bring it a little closer to the computer so I can get a better look at it..
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You have a Detroit 2 stroke diesel.. Detroit 2 strokes don't work like motorcycle two strokes you may be familiar with. I suggest you do a search and read up on how they work and why they dominated the Diesel market from 1930 until the EPA regulated them out of use.
4 53 means 4 cylinders in line, 53 cubic inches per cylinder. The two stroke Diesel Detroits require single weight oil, 40W or cold operation 30W, low ash content 3% or less, and the container needs to say it's formulated for Detroit 2 stroke engines.
If you are running multi weight oil, it does not have the viscosity to contain the oil as the pistons slide past the ports and it will pump oil out the block vent lines like mad.. or if the engine is getting tired.. it will pump oil out the vent lines.
Can't tell you which is your problem. I would start by putting the right oil in it and watch what happens. I suggest you make contact with your local Detroit service department. Not as many of the older 2 strokes are running now, but there are still guys that remember how to work on them and what parts they need.. Napa has Detroit proper oil, I just bought 9 gallons for my 8V92 powered motor home.